DE69717398T2 - Optical isomers of derivatives of campholene aldehyde - Google Patents

Description

The present invention relates to a mixture of the 4 diastereomers 1'S,2R,3S;1'S,2S,3R;1'S,2S,3S and 1'S,2R,3R of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol, a mixture of the 4 diastereomers 1'R,2S,3R;1'R,2R,3S;1'R,2R,3R and 1'R,2S,3S of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol and to (1'S,2S,3R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol, (1'R,2S,3R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol and to a process for preparing these compounds or mixtures. Furthermore, the invention relates to any isomer mixture of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol enriched with one or both of the compounds or mixtures, in particular to a fragrance composition containing any isomer mixture of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol enriched with one or both of the above compounds or mixtures, and to the use of any of the compounds or mixtures as fragrances. Here and below, the term "enriched" means that an excess of one or both of the two compounds or mixtures mentioned at the beginning is present in an isomer mixture of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol, i.e. that a certain isomer or mixture of isomers is present in a disproportionate amount. For example, a mixture of 4 diastereomers of (1'S)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol with enriched in the 1'S,2S,3R isomer if it contains more than 25% of said 1'S,2S,3R isomer.

Despite the numerous studies in the field of campholenic aldehyde derivatives, the prediction of the olfactory properties of different isomers, and in particular optical isomers, remains a difficult challenge. So far, it is not possible to predict which absolute configuration of carbon atoms of the five-membered ring and the side chains of such derivatives will elicit the strongest, most substantial and/or most natural sandalwood odor.

East Indian Sandalwood Oil has been described as "possibly one of the most valuable perfumery materials from ancient times to modern times, and there is no sign of its popularity diminishing" (E. Guenther in "The Essential Oils", D. Van Nostrand Company, Inc., New York, 1952, Vol 5. p 173). This oil is widely used in the perfume industry and would be even more widely used if supplies were not limited and costs were not high.

For many years there was a need for synthetic substitutes that could be used as sandalwood substitutes or as fillers.

The activities in the analysis of sandalwood oil and the search for synthetic substitutes have been extensively described (see E.-J. Brunke and E. Klein in "Fragrance Chemistry - The Science of the Sense of Smell", ET Theimer, ed., Academic Press, New York, NY 1982, p. 397; KH Shankaranarayana and K. Parthasarathi, Perfumer and Flavourist, 9, 17, (1984); G. Ohloff, Ch. Fehr in "Perfumes - Art, Science and Technology", PM Mueller, D. Lamparsky, ed., Elsevier Science Publishers, London, New York 1991, p. 298; G. Frater and D. Lamparsky, ibid, p. 561).

EP-A-203528 and US Patent No. 4,696,766 deal, inter alia, with the compound (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol of the formula

in particular with two pairs of enantiomers thereof. The compound has the olfactory properties of sandalwood. It has been shown that the olfactory properties of sandalwood of (E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol depend on its relative configuration (see below). Due to the three asymmetric centers (*) in the compound of formula I, eight optical isomers (four pairs of enantiomers) are expected. The compound was separated into a lower boiling and a higher boiling component by liquid/gas chromatography on a Carbowax® 20 M capillary column or by spinning ribbon distillation. Furthermore, liquid/gas chromatography analysis on an ethylene glycol succinate capillary column resolved each of these two components, confirming the presence of the four diastereomeric enantiomer pairs.

Thus, the disclosure relates to two lower boiling enantiomer pairs, e.g. 1'S*,2R*,3S* and 1'S*,2R*,3R*, and two higher boiling ones, e.g. 1'S*,2R*,3R* and 1'S*,2S*,3S*. The two lower boiling enantiomer pairs have been reported to be the organoleptically active compounds which have a very intense creamy, woody, musky sandalwood odor and are valuable ingredients for use in fragrance compositions because of their musky and sandalwood qualities. The mixture of these pairs of enantiomers is described as being more intense than any of the campholenic aldehyde derivatives previously described. However, nothing has been disclosed of the scent of the individual enantiomers of the two most interesting enantiomer pairs, i.e. 1'S*,2R*,3S* and 1'S*,2R*,3R*, as well as that of the other four stereoisomers which together form a successful perfumery raw material sold under the name Ebanol. It should be noted that the lower boiling enantiomer pairs described above are not commercially available.

The four enantiomer pairs are shown below:

As described in EP-A-203528, the mixture of diastereomers of compound 1 is prepared in a sequence of steps as outlined below.

Compound II is an α,β-unsaturated ketone which is converted to β,γ-unsaturated ketone III, which is then reduced to compound I by reduction of the ketone carbonyl to the corresponding alcohol.

Compound II is prepared from campholenic aldehyde by an aldol condensation, where the campholenic aldehyde is prepared from α-pinene via α-pinene epoxide. This is a well-known process in the art, see, for example, U.S. Patent No. 4,052,341.

It has now been found that the olfactory properties of each of the individual optical isomers of this eight-component mixture are crucial for developing a better (but still commercially viable) version of the composition enriched with the more valuable isomer(s). This can significantly improve the quality of the commercialized raw material by providing more and better odor for the same weight, which is important not only for economic reasons, but also for environmental reasons.

In the synthesis of compound I according to the reaction described above, the configuration of the starting material campholenic aldehyde depends on that of α-pinene, which determines the configuration of the C1' atom of the final product. The configuration of the two other asymmetric carbons of the compound, located in the side chain, namely C2 and C3, is more difficult to influence, but can be resolved by rapidly developing asymmetric synthesis methods or by relatively simple separation of the diastereomers. A systematic application of this knowledge leads to the isolation of each of the eight stereoisomers that make up compound I. In this way, the organoleptic properties of each of the stereoisomers could be determined.

The foregoing is shown schematically in Fig. 1 and 2. When (1R)-(+)-α-pinene is used to prepare campholenic aldehyde via pinene epoxide, the product is (S)-(-)-campholenic aldehyde. When this campholenic aldehyde is used as the starting material for the preparation of compound II and the reaction is carried out as described above (as shown in Fig. 1 shown in the upper part), the four diastereomers 1a, 1b, 1c and 1d of compound 1 are prepared.

On the other hand, if (1S)-(-)-α-pinene is used to prepare campholenic aldehyde via pinene epoxide, the product is (1R)-(+)-campholenic aldehyde. If this campholenic aldehyde is used as a starting material for the preparation of compound II and the reaction is carried out as described above (as shown in Fig. 1 in the upper part), the other four diastereomers, namely 2a, 2b, 2c and 2d of compound 1 are prepared. After the stereoisomers are separated by flash chromatography to obtain 2 pairs of diastereomers, they are further separated by gas chromatography as shown in Fig. 2. The final reduction of ketone III can be carried out asymmetrically (e.g. using L-selectride), which preferentially yields the two first eluted diastereomers or diastereomeric pairs of the enantiomers: 1a + 1b or 2a + 2b. Thus, if in the starting material the enantiomeric excess is different from 100%, two diastereomeric pairs of enantiomers 1a + 1b and 2a + 2b are preferably obtained, as shown in Example 2, where the isomers (1'S*,2R*,3S*) and (1'S*,2S*,3R*) constitute 79% of the product. In addition, Fig. 2 shows the relevance of the sandalwood odor as measured for each of the stereoisomers by determining its odor threshold.

The odour threshold is a physical property of the composition and is defined as "its lowest concentration in the air which can be consistently distinguished from pure air" (JE Amoore in "Fragrance Chemistry - The Science of the Sense of Smell", ET Theimer, ed., Academic Press, New York, NY, 1982, p. 34). The odor threshold is expressed in words as the weight of odorant per unit volume of air, as determined by olfactometry, a technique known to those skilled in the art and discussed by Amoore. Essentially, the odor threshold is the smallest amount of an odorant that must be present in order to be detected in a unit volume of air, that is, to be distinguished from the air itself.

Details of the procedure and the results are described below and explained in examples.

Four diastereomeric pairs were synthesized and evaluated as such using the gas chromatography sniff technique, which allows to smell both of the two diastereomers of each pair separately. In this way, odor profiles and GC (gas chromatography) odor thresholds of all eight optical isomers of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol were obtained. The results are quantified in Fig. 2. Unexpectedly, only one isomer of the two enantiomers of both enantiomeric pairs 1'S*,2R*,3S* and 1'S*,2S*,3R* was found to be the carrier of the strong natural sandalwood odor, namely 1'S,2S,3R and 1'R,2S,3R. These stereoisomers can all be obtained in pure form. The odor intensity ratio between these two best stereoisomers (1'S,2S,3R, 1'R,2S,3R) is ~3-5 : 1. Their odors are by far the strongest and they are apparently the only ones of the eight components of the blend that give it the natural, warm, lactonic scent of the sandalwood type. This shows that in this case the shape of the side chains, as determined by the absolute configuration of the C2 and C3 Carbons, plays a key role in the perception of sandalwood odor and is more important than that of the asymmetric carbon of the carbon ring.

The term "in pure form" in the present context refers to a material which is essentially free of further stereoisomers, preferably with at least 90% optical purity, more preferably with at least 95% optical purity.

The assignment of the absolute configuration of all stereoisomers cited in this paper is based on the GC retention time of diastereoisomeric pairs of enantiomers, as in US Patent No. 4,696,766, and on the knowledge of the absolute configuration of the starting material. (S)-(-)-campholenic aldehyde and its (R)-(+)-enantiomer were synthesized according to the known procedure starting from (1R)-(+) and (1S)-(-)-α-pinene, respectively. The pinenes with an enantiomeric excess (ee) of > 98% were provided by Aldrich. The campholenic aldehyde of Example 2 was obtained from an industrial grade of (1R)-(+)-α-pinene with ee = 43%. The optical purity of the enantiomers of campholenic aldehyde was measured by gas chromatography using an OV-1701/octakis(6-methyl-2,3-dipentyl)-γ-cyclodextrin chiral stationary phase and confirmed the ee of the pinenes. Gas chromatography analyses of the reaction products and intermediates were carried out on a Megabore DB 5 30 m x 0.53 mm column. Optical rotation measurements were performed on a Perkin-Elmer 241 polarimeter. The structure of the enantiomerically pure compounds and mixtures of diastereomers described in the examples, was examined by their ¹H and ¹³C NMR, IR and mass spectra, as well as those of the corresponding enantiomeric mixtures described in the above-mentioned US Patent No. 4,696,766. All synthesized products are colorless oils.

example 1 Preparation of (1'S)-(E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol and separation of its stereoisomers. a) (1'S)-(E)-3-Methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-3-en-2-one

This compound was obtained as the corresponding enantiomeric mixture of Example II-1 of US Patent No. 4,052,341 starting from 18.0 g of (S)-(-)-campholenic aldehyde and 52.1 g of butan-2-one and purified by distillation on a 5 cm Vigreux column. Yield: 15.1 g (62%). The product contained small amounts of other isomers but was used in the next step without further purification.

b) Preparation of (1'S)-(E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-one

7.0 g of ketone from Example 1a) was added dropwise over 30 min to a stirred solution of 5.9 g of potassium tert-butoxide in 35 ml of dimethylformamide (DMF) at 10°C. The yellow reaction mixture was stirred for 5 h at room temperature, then cooled to 0°C, treated rapidly with 25 ml of 20% aqueous acetic acid and extracted with 200 ml of methyl tert-butyl ether. The extract was washed with 2 x 50 ml of water, dried (MgSO₄) and concentrated in vacuo to give 5.2 g of crude product as a slightly yellow oil. Purification by flash chromatography on silica gel using a methyl tert-butyl ether/hexane 1:15 mixture as eluent gave 2.7 g (39% yield) of (1'S)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-one. GC purity: 96%; [α]D²² = +51.5º (c. 1.03, ethanol).

c) Preparation of (1'S)-(E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol

A solution of 1.5 g of the β,γ-unsaturated ketone of Example 1b) in 10 ml of pure ethanol was added dropwise at -5°C and under nitrogen to 0.3 g of sodium borohydride suspended in 20 ml of the same solvent. Stirring was continued for 20 h at r.t., then the reaction mixture was poured onto 150 ml of ice-cold 0.1 N hydrochloric acid and extracted with 2 x 100 ml of MTBE. The extract was washed with 2 x 100 ml of brine, dried (MgSO4) and concentrated in vacuo to give 1.5 g of 93% GC pure product (~ quantitative yield) as a colorless oil.

d) Separation of the stereoisomers of (1'S)-(E)-3-methyl-5- (2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol

1.5 g of the crude product from the previous step were separated by flash chromatography on silica gel using a methyl tert-butyl ether/hexane 1:5 mixture as eluent. Two fractions containing only two components each were isolated:

Fraction 1 (0.5 g; GC purity: > 95%) contains ~3 : 2 mixture of isomers (1'S,2R,3S) and (1'S,2S,3R);

[α]D²² = +24.5º (c. 1.01, ethanol); Odor: sandalwood, dry, green, strong.

Fraction 2 (0.25 g; GC purity: > 95%) contains ~1 : 1 mixture of isomers (1'S,2S,3S) and (1'S,2R,3R);

[α]D²² = +27º (c. 0.99, ethanol); Odor: celery, floral, fruity, green.

More of each isomer could have been isolated from the less pure fractions. Both pure fractions were separated by gas chromatography on the ethylene glycol succinate (LAC-4R-886) 39 m · 0.3 mm glass capillary column. Their components were evaluated using the GC-Sniff technique. The odor quality and the odor threshold values of the individual molecules are shown in detail in Fig. 2.

Example 2 Preparation of (E)-3-methyl-5-(2,2,3-trimethylcyclopent- 3-en-1-yl)pent-4-en-2-ol containing ~28% of the isomer (1'S,2S,3R)

22 ml of a 1M solution of L-Selectride in tetrahydrofuran (THF) was added dropwise, under nitrogen, at 0-5°C with stirring, into 4.1 g of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-one, which was prepared according to Example 1b from an industrial grade of (S)-campholenic aldehyde (ee 43%) and dissolved in 40 ml of the same solvent. The reaction mixture was left to warm to room temperature and stirring was continued for 4 h. 20 ml of methanol and 200 ml of brine were added successively and the aqueous phase was extracted with 3 x 200 mL of methyl tert-butyl ether (MTBE). The combined organic layers were dried (MgSO4), the solvent was concentrated in vacuo and the residue was purified by flash chromatography (MTBE/hexane = 1/4) followed by bulb-to-bulb distillation at 0.1 Torr. The product (2.8 g; 67% yield) contained 40, 39, 4.5 and 6.5% diastereomeric pairs of enantiomers (1'S*,2R*,3S*), (1'S*,2S*,3R*), (1'S*,2S*,3S*) and (1'S*,2R*,3R*), respectively, the enantiomeric ratio of each pair was 1'S/1'R = 71.5:28.5; [α]D²² = + 10.5° (c. 1.00, ethanol).;

Smell: woody, sandalwood, amber-like with cedarwood and pine needle aspects, stronger and finer than Ebanol

Example 3 Preparation of (1'R)-(E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol and separation of the stereoisomers.

The following (1'R) enantiomers were prepared starting from (R)- (+)-campholenic aldehyde in the same manner as their (1'S) analogue of Example 1:

a) (1'R)-(E)-3-Methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-3-en-2-one

b) (1'R)-(E)-3-Methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-one

GC purity: 98%; [α]D²² = - 52.5º (c. 1.06, ethanol).

c) (1'R)-(E)-3-Methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol

d) Separation of the stereoisomers of (1'R)-(E)-3-methyl-5- (2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol

1.5 g (almost quantitative yield) of the crude product from the previous step was separated by flash chromatography on silica gel using a methyl tert-butyl ether/hexane 1:5 mixture as eluent. Two fractions containing only two components each were isolated:

Fraction 1 (0.5 g; GC purity: 91%) contains ~3 : 2 mixture of isomers (1'R,2S,3R) and (1'R,2R,3S);

[α]D²² = -25.5° (c. 1.15, ethanol);

Odour: creamy, milky, sweet, sandalwood, weaker than that of the corresponding fraction 1 of Example 1d

Fraction 2 (0.32 g; GC purity: > 95%) contains ~1 : 1 mixture of isomers (1'R,2R,3R) and (1'R,2S,3S);

[α]D²² = -24.5° (c. 1.01, ethanol);

Smell: celery, woody.

More of each isomer could have been isolated from the less pure fractions. Both pure fractions were separated and evaluated. Odor quality and odor thresholds were determined as in Example 1d using the GC-sniff technique shown in Fig. 2.

Example 4

This example shows the advantage of the isomers according to the invention compared to Ebanol, the prior art product, which is a commercialized isomer mixture of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol. A fine fragrance containing the following ingredients was prepared.

Ingredients Quantity [g]

C-11 Aldehyde (undecyclic) 10% gel. in DPG 0.3

Allylamyl glycolate 0.4

Benzyl acetate 1.0

Benzyl salicylate 2.0

Bergamot Oil Base 8.0

Cardamom oil (Ceylon) 0.2

Cassione (Firmenich), 10% gel. in DPG 0.5

Citronellyl acetate 0.5

Coumarin crystallized 0.5

Cyclal C, 10% gel. in DPG 0.5

Dipropylene glycol 10.6

Ebanol 1.0

Galaxolide, 10% gel. DEP 20.0

Geraniol 0.8

Hedion 21.0

Cis-3-Hexenyl Salicylate 3.0

Indoles, 10% gel. in DPG 0.3

Iso E super 4.0

Cis-jasmone, 10% gel. in DPG 0.6

Linaloolsynth. 6.0

Linalyl acetate 4.0

Mandarin Oil (Restoration) 5.0

Patchouli Oil 2.5

Phenylethanol 4.5

Stemon 0.3

Vanillin 2.5

100.0g

(DPG = dipropylene glycol; DEP = diethyl phthalate)

If the quality of the ebanol used in this composition is improved by using twice less (by weight) of the 3 : 2 mixture of (1'S,2R,3S) and (1'S,2S,3R)- (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4- en-2-ol of Example 1d, the sandalwood hue of its odor was maintained and even enhanced. The sandalwood aspect was thus accentuated, using less of the product.

Example 5

A fragrance for a detergent powder or a softener was prepared with the following ingredients and compared with the same fragrance, but containing the isomers of fractions 1 of Example 1d instead of ebanol.

Ingredients Quantity [g]

Agrumex 5.0

C-12 Aldehyde (MNA) 0.03

C-11 Aldehyde (iso) 0.07

Allylcyclohexylpropionate 2.0

Anther 1.0

Bergamot Oil Base 8.0

4-tert-butylcyclohexyl acetate 10.0

Citronellol 4.0

Dihydromyrcenol 3.0

Dipropylene glycol 3.0

Dimethylbenzylcarbinyl acetate 4.0

Ebanol 2.0

Eucalyptus globulus oil (China) 0.5

Geranyl acetate 1.5

Fixolide 7.0

cis-Hexenol 0.3

α-Hexylcinnamaldehyde 15.0

β-Ionone 3.0

Iso E super 2.0

Isoraldeine 70 7.0

cis-Jasmone 0.1

Lilial 6.0

Nonadyl 1.0

Rose oxide 0.5

Stemon 0.5

Undecavertol 0.5

Verdyl acetate 8.0

Verdyl Propionate 4.0

Viridine 1.0

100.0g

When comparing the two fragrances, the same effect as in Example 4 was observed on the damp and dried linen after washing and rinsing cycles.

The systematic chemical names of the trivial names of the individual components mentioned above are listed in standard works, e.g. in Flavour and Fragrance Materials 1996, Allured Publishing Corporation, Carol Stream, Illinois, USA or Arctander, Perfume and Flavor Chemicals - 1969, published by the author, Montclair, New Jersey, USA.

Claims (12)

1. An isomeric mixture of (E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol enriched in 1'S,2R,3S; 1'S,2S,3R; 1'S,2S,3S and 1'S,2R,3R diastereomers or an isomeric mixture of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1- yl)pent-4-en-2-ol enriched in 1'R,2S,3R- 1'R,2R,3S; 1'R,2R,3R; and 1'R,2S,3S diastereomers. 2. A stereoisomer (1'S,2S,3R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol or ( 1'R,2S,3R)-(E)-3-Methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol. 3. A stereoisomer according to claim 2 which is at least 90% optically pure. 4. An isomer mixture of (E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol enriched with one of the compounds according to claim 2. 5. A process for preparing a mixture according to claim 1 or a compound according to claim 2 characterized in that the mixture or the compound is synthetically prepared. 6. A process for preparing a mixture according to claim 1 comprising using (1'S)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)-pent-4-en-2-one as a suitable starting material and reducing it to (1'S)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol; or (1'R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-one as a suitable starting material and reducing it to (1'R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol. 7. A process for preparing a stereoisomer according to claim 2 or claim 3, comprising using (1'S)-(E)-3-methyl-5-(2,2,3- trimethylcyclopent-3-en-1-yl)pent-4-en-2-one as a suitable starting material and reducing it to (1'S)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3- en-1-yl)pent-4-en-2-ol, wherein the intermediate is a mixture of the diastereomers 1'S,2R,3S; 1'S,2S,3R and 1'S,2S,3S; 1'S,2R,3R, separating the mixture of diastereomers and isolating the isomer 1'S,2S,3R; or from (1'R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-one as a suitable starting material and reducing it to (1'R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol, wherein the intermediate is a mixture of the diastereomers 1'R,2S,3R; 1'R,2R,3S and 1'R,2R,3R; 1'R,2S,3S, the mixture of diastereomers is separated and the isomer 1'R,2S,3R is isolated. 8. The process according to claim 6 or 7, characterized in that the starting material (1'S)-(E)- 3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent- 4-en-2-one is synthesized from (S)-(-)-campholenic aldehyde according to a known method; and the starting material (1'R)-(E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-one is synthesized from (R)- (+)-campholenic aldehyde according to a known method. 9. The use of the mixture according to claim 1 or 4 or the stereoisomer according to claim 2 or 3 as a fragrance. 10. A fragrant composition containing any isomer mixture of (E)-3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol enriched with at least one of the mixtures according to claim 1 or 4 and/or at least one of the stereoisomers of claim 2 or 3. 11. Process according to one of claims 6, 7 and 8, characterized in that the starting material is present in an enantiomeric excess. 12. Process according to claim 11, characterized in that the reduction of the starting material is carried out in an asymmetric manner.